This invention relates to poppet check valves, in particular for resisting backflow.
A typical prior art poppet check valve 10, shown, e.g., in FIGS. 1 and 2, has a valve element 12 positioned for engagement upon an opposed valve seat 14 to resist flow through an orifice 11 defined by the seat until the pressure of the flow exceeds a predetermined value and lifts the valve element from the seat. In the typical prior art poppet valve 10, the valve element 12 is biased toward the valve seat 14 by an axially aligned compression spring 16 disposed about the valve stem 13 and bearing against a pin 15. As a result, as the valve element 12 is displaced from the seat 14, e.g. by fluid flowing through the orifice in the direction of arrow, F.sub.w, the spring 16 is compressed (FIG. 2), thus causing the spring 16 to exert a spring load, F.sub.s, that increases with displacement distance, D, of the valve 12 from the seat 14, thereby creating a larger pressure drop across the valve opening.
In another type of check valve, e.g. as described in Habiger U.S. Pat. No. 4,072,167, an arm of a centrally fixed torsional spring biases a ball in the valve against a valve seat. As the ball moves away from the valve seat, the arm of the spring rotates with respect to the ball to compress the spring.
In another type of valve, e.g. as described in Smith U.S. Pat. No. 711,792, two bow-springs each exert a vertical force against opposite edges of a valve element to bias the element against a valve seat. The vertical force exerted by the bow-springs increases with the displacement of the valve element away from the valve seat.